Active array antennas, implemented as Direct Radiating Array, in front of a reflector or in a discrete lens antenna, are characterized by high flexibility. However, their poor power efficiency, high cost and deployment complexity with respect to passive reflectors or passive array antennas have hindered their implementation in several applications and, in particular, in satellite missions. Today, active array antennas are employed in satellite applications mainly when antenna beam electronic reconfigurability is needed.
Recently, solutions based on aperiodic arrays with equi-amplitude or stepped amplitude elements have been considered in order to reduce the complexity and the cost of traditional periodic arrays when generating a multibeam coverage within an assigned limited field of view or a number of beams to be electronically steered within a limited field of view [1-5]. In fact, non regular filled apertures with equi-amplitude or stepped amplitude elements allow maximizing the Amplifiers Power Added Efficiency (in transmission); reducing the complexity and the required number of active controls; and reducing the sidelobes and grating lobes even using large average spacing between contiguous elements.
The achievable reduction in the number of radiators strongly depends on the requested sidelobe level and on the extension of the field of view where the pattern should be controlled [5]. Large non regular (aperiodic) arrays are characterized by inter-element distances exhibiting a large dynamic; as a consequence, in order to guarantee a good aperture efficiency, radiators with different dimensions should be employed. This means that small radiators may be used in the areas of the aperture where the inter-element distances are small, while larger elements may be used in areas characterized by large inter-element spacing. This increases the aperture efficiency, allowing a large fraction of the array surface contributing to the emission or reception of electromagnetic waves.
The design of non regular arrays is usually done considering only a single nominal pointing direction for the beam, frequently coinciding with the boresight direction. When the main beam is pointed out of this direction, severe scan losses are experienced especially because of the directive radiation patterns associated to the largest radiators composing the array. As a consequence, large non regular arrays characterized by a minimized number of controls exhibit scanning losses much higher compared to the cos θ-like scan losses typical of continuous apertures and densely populated arrays.
A similar problem arises with a multibeam pattern, comprising at least one beam pointing away from the boresight direction, and with shaped beams covering a broad field of view.